Superhydrophilic and antifogging non-porous TiO2 films for glass and methods of providing the same

ABSTRACT

Superhydrophilic and antifogging non-porous TiO2 films for glass substrates and methods of providing the TiO2 films are provided. The TiO2 films may maintain a water contact angle less than 5° in the dark for five days after an annealing treatment, and the water contact angle of the TiO2 films may stabilize at less than 20° after ten days from the annealing treatment. The TiO2 films may have a thickness of about 20 nm and may be transparent. The methods may include depositing a TiO2 film on a glass substrate using e-beam evaporation. The methods may further include annealing the TiO2 film after depositing the TiO2 film on the glass substrate. The methods may not include UV radiation.

REFERENCE TO PRIORITY APPLICATION

This application is related to and claims the priority of U.S.Provisional Application Ser. No. 62/382,278, entitled METHOD FOR THEPRODUCTION OF SUPERHYDROPHILIC AND ANTIFOGGING PROPERTIES OF NON-UVACTIVATED, NON-POROUS TIO2 FILMS ON GLASS, filed in the USPTO on Sep. 1,2016, the entire disclosure of which is incorporated herein byreference.

BACKGROUND

Keeping glass clean from fogging up is one of growing interests amongglass manufacturers and suppliers. Anti-fog glass is becoming more andmore prevalent in day to day products such as bathroom mirrors, carwindows, eye glasses, etc. Having anti-fog glass may increase safety inmany instances such as in cars. When there is humidity or a rapidtemperature change, fogging glass may disrupt the driver's ability tosee through their windscreen or to see views in side view mirrors. Inother applications, anti-fog glass may eliminate the inconvenience offogging in kitchen and bathroom glass and mirrors caused by hot showersand boiling water. There are many other places and circumstances whereanti-fog glass may help safety and convenience, such as on facade glassin the presence of a significant temperature gradient and highenvironmental humidity.

Because of the synergetic effect of photocatalysis and photo-inducedhydrophilicity of titanium oxide (TiO₂), TiO₂ has been considered as agood candidate for a large-scale and relatively inexpensive applicationsin the fields of antifogging and self-cleaning coatings. It is knownthat TiO₂ hydrophilic surfaces can be obtained by UV activation througha redox mechanism that results in trapping of the photo-generated holesat lattice sites and subsequent Ti—O bond rupture by adsorbed watermolecules, and forming new hydroxyl groups. The rapid advance in surfacescience and the increasing industrial demand has significantlyfacilitated the development of anti-fogging and self-cleaning engineeredsurfaces showing a superhydrophilic character without any externalstimuli, in which titanic is combined with other materials such as inthe case of multilayer assemblies constituted by TiO₂ nanoparticles andpolyethylene glycol or yet porous ZnO/TiO₂ composite films.

Few studies deal with the fabrication of coatings made exclusively byTiO₂ and superhydrophilic without radiation. Existing methods includethe preparation of porous TiO₂ nanostructures by a sol-gel method,exhibiting stable super-wetting properties without the need of lightactivation. Other methods include fabricating perpendicular TiO₂nanosheet films by a hydrothermal treatment of a titanium metal sheetwith aqueous urea, resulting in superhydrophilicity without UVirradiation due to the enhanced density of oxygen defects or danglingbonds present in these structures.

Many attempts have been made to control the wettability by tuningcoating porosity and roughness, which may allow water to rapidlypermeate the three-dimensional porous network that induces the completewetting of the surface. Porous films, containing a mixture of all themain three polymorphs of TiO₂, have previously been synthetized bysupersonic aerosol deposition. These films became superhydrophilicwithout UV illumination after high-temperature annealing. Porousstructures may not meet the requirements of high transparency in thevisible region due to the high surface roughness dramatically depletingthe transmittance of the coatings seriously affected by an enhanceddiffuse scattering. In addition, their mechanical properties may bepoorer than those of compact films and thus those may not be used aslong-lasting building materials.

SUMMARY

According to some embodiments of the invention, a coated glass mayinclude a glass substrate and a TiO₂ film on the glass substrate. TheTiO₂ film may maintain a water contact angle less than 5° in the darkfor five days after an annealing treatment.

In some embodiments, the water contact angle of the TiO₂ film maystabilize at less than 20° after ten days from the annealing treatment.In some embodiments, the water contact angle of the TiO₂ film may beless than 5° for eight days from the annealing treatment and UV-exposureand may stabilizes at less than 15° after fifteen days from theannealing treatment and UV-exposure. In some embodiments, the TiO₂ filmmay have a thickness of about 20 nm. The coated glass may have opticaltransmittance greater than 85% at wavelength higher than 350 nm, andoptical transmittance of the coated glass may be similar to opticaltransmittance of the glass substrate (i.e., a bare glass) at wavelengthhigher than 350 nm.

In some embodiments, the coated glass may show high water spreadingafter exposure to humid indoor air following 2 hours in the deep-freezeat −15° C., thereby reducing or possibly preventing glass fogging andensuring its transparency in the visible range. According to someembodiments of the invention, a coated glass may include a glasssubstrate and a TiO₂ film on the glass substrate. The TiO₂ film may havea grain size of from about 30 nm to about 50 nm.

According to some embodiments of the invention, a method of providing acoated glass may include depositing a TiO₂ film on a glass substrateusing e-beam evaporation. In some embodiments, the method may furtherinclude annealing the TiO₂ film after depositing the TiO₂ film on theglass substrate.

In some embodiments, annealing the TiO₂ film may be carried out in air.In some embodiments, depositing the TiO₂ film may include rotating theglass substrate and may be carried out after a base pressure reaches atabout 3.0×10⁻⁶ Torr. Depositing the TiO₂ film may be carried out whilemaintaining a constant evaporation rate of about 1 Å s⁻¹. In someembodiments, depositing the TiO₂ film may be carried out at anaccelerating voltage of about 10 kV with a filament current of about26.5 A and emission current in a range of about 55 mA to about 65 mA.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates emission of a lamp during degradation tests.

FIG. 2A shows images showing contact angles of an as-deposited TiO₂ filmon a glass and an annealed TiO₂-GLASS. FIGS. 2B and 2C show images and agraph showing time evolution of contact angels of the annealed TiO₂ filmin the absence of applied radiation. FIG. 2D shows images providingcomparison between a bare glass, commercial product and annealedTiO₂-GLASS.

FIG. 3 shows XRD patterns of annealed TiO₂-GLASS and as-depositedTiO₂-GLASS.

FIGS. 4A, 4B, and 4C show variations of contact angle of tested glassesover time. FIG. 4A shows variations of contact angle of an UV-unexposedTiO₂-GLASS, FIG. 4B shows variations of contract angle of apreliminarily UV-exposed TiO₂-GLASS, and FIG, 4C shows variations ofcontact angle of a commercial product.

FIGS. 5A, 5B, 5C, and 5D show images of micro-scale wettabilitycharacterization by ESEM. FIG. 5A and FIG. 5B are micrographs of thecommercial product before and after the vapor pressure increase from 600to 765 Pa, respectively. FIG. 5C and FIG. 5D are micrographs ofTiO₂-GLASS before and after the vapor pressure increase, respectively.

FIG. 6A shows an AFM image, and FIG. 6B shows SEM micrograph ofTiO₂-GLASS.

FIGS. 7A and 7B depict size distribution of particles in water sampleswithdrawn from the beaker containing the 20-TiO₂-GLASS (FIG. 7A) andfrom the beaker containing the bare glass (FIG. 7B) after ultrasoundtreatment.

FIG. 8 shows Raman spectra of the adhesive tape before and afterdetachment from 20-TiO₂-GLASS.

FIGS. 9A and 9B show optical image of 20-TiO₂-GLASS (FIG. 9A) and thecommercial product (FIG. 9B) after the cross--cut test according to ISO2409 standard.

FIG. 10 shows storage moduli of bare annealed glass and 20-TiO₂-GLASS.

FIG. 11 illustrates Raman spectra of TiO₂-GLASS and the commercialproduct.

FIGS. 12A, 12B, and 12C depict antifogging and optical properties ofbare glass, 20-TiO₂-GLASS and the commercial product. FIG. 12A showsthree samples that appeared transparent before the anti-fogging test.FIG. 12B shows anti-fogging characters of bare glass, 20-TiO₂-GLASSafter two months from the thermal treatment and the commercial product.FIG. 12C depicts a comparison graph showing UV-vis transmittance data ofthe commercial product and the glass before and after the application ofa 20 nm-thick layer of TiO₂.

FIG. 13A shows UV-vis transmittance spectra, and FIG. 13B showsrefractive index of a 250 nm TiO₂ film deposited on glass.

FIGS. 14A and 14B show reactivity results of 20-TiO₂-GLASS,outdoor-exposed 20-TiO₂-GLASS (O.E. 20-TiO₂ -GLASS) and commercialproduct. FIG. 14A shows the concentrations of methanol and formaldehydemonitored over the time, and FIG. 14B shows the concentrations of2-propanol and acetone monitored over the time.

DETAILED DESCRIPTION

TiO₂ films according to some embodiments of the present invention may benon-porous films such that their surfaces are microscopically flat andsmooth down to the molecular level and may not allow water to passthrough those.

As used herein, the expression “in the dark” refers to a milieu in theabsence of UV light with a weak visible radiation coming from thesurrounding indoor environment, which is measured and found to be about0.3 W m⁻² in the range 450-950 nm.

As used herein, “root mean square (RMS) roughness” refers to the rootmean square average measured height deviation taken or measured withinan evaluation length or area. “root mean square (RMS) roughness” is alsodiscussed in, for example, U.S. Patent Application Publications No.US20120256201, US 20140049822, and US20160204343.

As used herein, “water contact angle” refers to the angle of contactbetween a drop of water and the surface of interest as a measure of thetendency for the water to spread over or wet the solid surface. Thelower the contact angle, the greater the tendency for the water to wetthe solid, until complete wetting occurs at an angle of zero degrees.“Water contact angle” is also discussed in, for example, U.S. PatentApplication Publications No. US20100304338, US20120026457, andUS20130118127.

As used herein, the term “about” refers to a value that is 20%, 15%,10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% ofthe stated value, as well as values intervening such stated values. Forexample, the phrase “about 200” includes ±20% of 200, from 160 to 240.

Throughout the specification, glass functionalized by the e-beamdeposited TiO₂ film according to some embodiments of the presentinvention is referred to as “TiO₂-GLASS”. Unless otherwise specified,the thickness of the TiO₂ film is 250 nm. The glass functionalized by a20 rim-thick TiO₂ film according to some embodiments of the presentinvention is referred to as “20-TiO₂-GLASS”.

As appreciated by the inventors, one of the possible routes to enhancethe wettability of TiO₂-based coatings is high-temperature annealingtreatment. Annealing may modify the crystal structure of TiO₂films andtheir surface chemistry and thus may improve hydrophilic properties ofthese films. Specifically, annealing may improve hydrophilic propertiesby producing oxygen vacancies, increasing roughness and eliminatingorganic impurities. Therefore, according to some embodiments of thepresent invention, superhydrophilic TiO₂ films may be provided usingradiation-free methods which do not use radiation (e.g., UV radiation).

According to some embodiments of the present invention, Ti), thin filmsmay be deposited by e-beam evaporation, and this technique may providean atom efficient, cost effective way of fabricating innovativenanostructures in large-scale industrial plants, as compared with othermethods, such as sol-gel processes. The functionalization of glass withsuch thin TiO₂ films may be able to produce optically transparent,self-cleaning and antifogging glass. The implications of thisbreakthrough may go behind this application, being beneficial in anysituation where flat condensation of water is desirable, as for instancein environmental humidity capture.

According to some embodiments of the present invention, methods ofproviding a TiO₂ coating (e.g., film) using e-beam evaporation areprovided, and the methods may be used to provide self-cleaningsuperhydrophilic glass. A TiO₂ coating deposited using e-beamevaporation may be annealed at 500° C., and the annealed TiO₂ coatingmay be a non-porous film that exhibits radiation-free superwettingbehavior ascribed to the high number of oxygen vacancies therein alongwith its crystallinity. The superhydrophilic and antifogging propertiesof the TiO₂ coating, which can be reactivated by a thermal treatment orprolonged through UV exposure, may provide potential applications toboth outdoor and indoor applications. The TiO₂ coating having athickness of about 20 nm may not alter the optical and mechanicalproperties of glass on which the TiO₂ coating is deposited. In addition,adhesion of the TiO₂ coating to a substrate (e.g., glass substrate) maybe very effective. A 20 nm TiO₂ film provided by the methods accordingto some embodiments of the present invention may possess a betterphotocatalytic activity than a commercial self-cleaning glass. Themethod of providing TiO₂ coatings that have improved properties maybecome a breakthrough in designing multifunctional coatings for nextgeneration self-cleaning transparent coatings, along with moreapplications involving the use of a flat superhydrophilic andself-cleaning surface.

According to some embodiments of the present invention, methods ofincreasing the wettability of glass or similar surfaces are provided.The methods may include depositing a thin, non-porous film of TiO₂ usinge-beam evaporation with TiO₂ source on a clean glass surface under avacuum. In some embodiments, a base vacuum in a chamber, before thedeposition process, may be about 3.0×10⁻⁶ Torr and may be maintainedconstant during the deposition process. In some embodiments, the glassmay be rotated at 40 rpm during the deposition process. An evaporationrate may be, for example, about 1 Å s⁻¹. In some embodiments, theevaporation rate may be maintained constant at about 1 Å s⁻¹. In someembodiments, the accelerating voltage may be about 10 kV, and thefilament current may be about 26.5 A. In some embodiments, the emissioncurrent may be in a range of about 55 mA to about 65 mA throughout thedeposition process. In some embodiments, a thickness of the TiO₂ filmmay range from about 20 nm to about 250 nm.

In some embodiments, a TiO₂ film deposited using e-beam evaporation maybe annealed in air at a temperature of about 500° C. for about 4 hours.In some embodiments, a TiO₂ film deposited using e-beam evaporation maybe annealed by the following steps: heating up to 475° C. (a ramp rateof about 10° C./min) and annealing for 5 min at 475° C.; heating up to500° C. (a ramp rate of 2.5° C./min) and annealing for 4 hours at 500°C.

In some embodiments, deposited and annealed TiO₂ films may have compactnonporous structures. In some embodiments, deposited and annealed TiO₂films may have superwetting properties in the absence of UV activation.In some embodiments, deposited and annealed TiO₂ films may demonstratesuperior performance compared to a bare glass substrate and a commercialself-cleaning glass in its antifogging and optical properties.Superhydrophilic characteristics may arise from the deposition techniqueinducing a large amount of oxygen vacancies and may be further boostedby an annealing treatment. In some embodiments, the superhydrophiliccharacter may be maintained even when a TiO₂ film has a small thickness,for example, ranging from about 20 to about 50 nm. Adhesion of the TiO₂film to the glass substrate was confirmed by ultrasound stress test andcross-cut test performed according to ISO 2409 standard.

Photocatalytic activity of the TiO₂ film was assessed by degradation ofmethanol and 2-propanol under UV light in a gas phase reactor, and theTiO₂ film showed superior performance to a commercial product.

In the Examples discussed below, a commercial product refers toPilkington Activ™, which is self-cleaning and photocatalytic glass.

EXAMPLE 1 Preparation of E-Beam Deposited TiO₂ films.

For film preparation, TiO₂ films were deposited on bare glasssubstrates, 25×75 mm soda-lime glass substrates (provided bySigma-Aldrich), by e-beam evaporation. Before the deposition, thesubstrates were ultrasound cleaned with acetone and isopropanol in twosuccessive 10-minute steps. :Pellets (size: 1-3 mm) made of TiO₂ (99.9%pure), which are provided by Plasmaterials, were used as sourcematerials in the Temescal BJD-2000 e-beam evaporation system. Typicalbase vacuum in the chamber before the deposition was 3.0×10⁻⁶ Torr. Thesubstrates were rotated at 40 rpm during the deposition and theevaporation rate was kept constant at 1 Å s⁻¹. The accelerating voltagewas 10 kV, and the filament current was 26.5 A. The emission current wasin a range of 55 mA to 65 mA throughout the deposition process. Filmshaving different thicknesses of from 20 nm to 250 nm were prepared.Stylus profilometer (Veeco Dektak 150) was used to confirm the filmthicknesses. After the deposition, the films were annealed in airthrough the following steps: heating up to 475° C. (ramp rate of 10°C./min) and annealing for 5 min at 475° C.; and heating up to 500° C.(ramp rate of 2.5° C./min) and annealing for 4 hours at 500° C.

EXAMPLE 2 Methods for Analysis of Structural and MorphologicalProperties of Non-Porous TiO₂ Films

Scanning electron microscopy (SEM, FEI Nova NanoSEM) was used to analyzemicrostructure of the deposited TiO₂ films, after sputtering a 5 nmlayer of Au Pd to the films. Atomic force microscopy (AFM) measurementswere performed using a Cypher AFM from Asylum Research (scan rate: 0.8Hz, integral gain: 10) to analyze topography of the films and theirroughness.

The crystal phase of the films were analyzed by XRD measurementsperformed with a Panalytical Empyrean system, using CuKα as radiationsource (1.5418 Å) at power settings of 45 kV and 40 mA. Diffractionpatterns were recorded in the range of diffraction angles 2θ from 20° to60° with a grazing angle of 3° and a scan rate of 0.075°/min.

Adhesion of the film to the glass substrate was investigated by checkingthe release of particles into water during ultrasound treatment.20-TiO₂-GLASS was cleaned in acetone and in ethanol in two successive5-minute steps. After these cleaning, and 20-TiO₂-GLASS was dried underArgon flow. 20-TiO₂-GLASS was dipped in a beaker containing DI waterwith a clock glass on top. The beaker was placed into an ultrasound bath(Falc, 100 W, 50 kHz) for 7.5 hours. A bare glass slide was placed inanother beaker and used as a control experiment. Before the test, thebeakers were left overnight with a 4M HCl solution inside and rinsedwith DI water many times in order to avoid the presence of anycontamination during the experiment. Water samples were withdrawn at 2.5and 5 hours and analyzed by a Z-sizer (ZetaPALS, Brookhaven) to verifythe possible presence of suspended particles. Afterwards the used waterwas replaced by fresh DI water after rinsing the 20-TiO₂-GLASS, bareglass and beakers. The ultrasound treatment was extended by other 2.5hours.

Adhesion of the film to the glass substrate was further tested by usingan adhesive transparent tape. After detaching the tape from the20-TiO₂-GLASS, the tape surface was analyzed by Raman Spectroscopy(Witec Alpha 300R equipment) to search for TiO₂ characteristic signals.

Adhesion tests were also carried out by adhesion (TQC model CC3000)tests according to the ISO 2409 standard. The incurrence of anyscratches following the tests was evaluated by an optical microscope(Olympus BX51M).

Dynamical Mechanical Analysis (DMA) was performed using a DMA 800analyzer from PerkinElmer. The 20-TiO₂-GLASS film was heated from roomtemperature to 250° C. at a heating rate of 3° C./min and frequency of 1Hz. The results were compared to those of the bare glass annealed at500° C.

The hydrophilic properties of the films were evaluated by a Kruss EasyDrop Contact Angle analysis machine. After annealing, TiO₂-GLASS wascleaned in acetone and then in ethanol in two successive 5-minute stepsand finally dried under Argon flow. Eventually, samples were heated at50° C. for 30 min in order to allow for the volatile organic residues tobe removed. Glass substrate and a commercial product underwent the sametreatment prior to measure the contact angle. On each sample, fiveconsecutive measurements were performed to report a reliable averagecontact angle. The drop volume was 5 μL. In some cases, 30 min UV-visirradiation was provided by a 500 W Mercury-Xenon lamp connected to anoptical fiber, before measuring the contact angles. The average valuesof radiation intensity reaching the surface of bare and functionalizedglass samples, measured with a Delta Ohm 9721 radiometer and thematching probes, were 33.4 W m⁻² in the range 200-280 nm, 75 W m⁻² inthe range 280-315 nm, 54 W m⁻² in the range 315-400 nm, and 131 W m⁻² inthe range 450-950 nm. Hydrophilic properties of the functionalized glasswere also assessed after being exposed to outdoor environment in AbuDhabi for one month (Aug. 18, 2016-Sep. 17, 2016).

The investigation of wettability properties at the micro-scale wasperformed by using an Environmental SEM (FEI, Quanta 250). The samplewas cooled down to 1° C. while keeping the chamber pressure at 100 Pa,After 1 hour, the pressure was raised slowly to 600 Pa, waiting for thesystem to be in equilibrium. Water condensation was reached by furtherincreasing the pressure up to 750 Pa. The sample stage was tilted of5-10° in order to increase the droplets counts. The contact angle ofdroplets was then measured by using the software, Image J.

Raman spectroscopy was run by a Witec Alpha 300R equipment, with anexcitation wavelength of 532 nm and a laser power of ca. 75 mW. Scanswere taken over an extended range (100-800 cm⁻¹).

Antifogging properties were evaluated after placing the samples in afreezer at −15° C. for 2 hours, followed by exposure to indoorenvironmental atmosphere. Digital images were taken to qualitativelycompare air humidity condensation on bare glass, 20-TiO₂-GLASS and acommercial product. Optical transmittance of the samples was measured bya UV-Vis spectrophotometer (Shimadzu UV-2600) in the 200-800 nm range.

Referring to FIG. 1, it illustrates the emission of the lamp used duringthe degradation tests on methanol and 2-propanol: a 50 W LED source wasused with a UV emission centered at 385 nm. The average values of theradiation reaching the sample surface were 30.4 and 24.4 W m⁻² in the315-400 and 450-950 nm ranges, respectively. The reactivity runs wereperformed in a 341 mL gas-phase reactor made of Pyrex glass and anexternal jacket in which water circulated continuously during thereaction to keep the temperature constant at ca. 22° C. Before injecting0.5 μL of liquid methanol (ca. 11.5 μmol) and 2-propanol (ca. 6.2 μmol)in two different tests, the reactor was saturated with oxygen bycontinuously flowing for 30 min. After injection of the target moleculesand before turning the lamp on, 10 min has elapsed to reach theadsorption/desorption thermodynamic equilibrium. During irradiation, thephotoxidation of methanol and 2-propanol and the formation offormaldehyde and acetone, respectively, were assessed by a gaschromatograph (Shimadzu GC 2014). The gas chromatograph was equippedwith a flame ionization detector and a Phenomenex column ZebronZB-WAXplus 30 m L×0.32 mm ID. N₂ was used as the carrier gas and thecarrier flow in the column was set at 1.60 mL min⁻¹. The columntemperature was 65° C., whereas the injector and detector temperatureswere 250° C. and 245° C. Photocatalytic activity of the outdoor exposedsample was also assessed.

EXAMPLE 3 Analysis of Hydrophilic and Wettability Properties ofNon-Porous TiO₂ Films

FIG. 2A shows images showing contact angles of an as-deposited TiO₂ filmon a glass and an annealed TiO₂-GLASS. FIGS. 2B and 2C show images and agraph showing time evolution of contact angels of the annealed TiO₂ filmin the absence of applied radiation. FIG. 2D shows images providingcomparison between a bare glass, commercial product and annealedTiO₂-GLASS.

TiO₂-GLASS was found to be hydrophobic after deposition, with a watercontact angle (CA) of 90±7°, whereas, after annealing at 500° C., itappeared to be superhydrophilic with CA close to 0° with water spreadingcompletely and evenly upon the surface as shown in FIG. 2A. This largevariation in surface energy after the thermal treatment results from thegeneration of a large number of oxygen vacancies following the releaseof surface oxygen occurring upon the annealing/crystallization, makingthe surface more prone to adsorb water in a flat shape.

FIG. 3 shows XRD patterns of annealed TiO₂-GLASS and as-depositedTiO₂-GLASS. The thermal induced superhydrophilicity is fostered bychanges in structural properties as confirmed by the XRD pattern in FIG.3. After annealing, the films become crystalline and show the presenceof well-crystallized anatase phase.

The time evolution of the contact angle (CA) relative to the thermaltreated TiO₂-GLASS is shown in FIGS. 2B and 2C. It is critical toemphasize that no UV light was used during the experiment, and the weakvisible light of the surrounding environment was measured and found tobe 0.3 W m⁻² in the range 450-950 nm. All the measurements wereperformed using a water droplet of quite large volume (5 μL) in order tomonitor the spread pattern and uniformity over the film. AnnealedTiO₂-GLASS was found to reach a superhydrophilic state (CA<5°) very fastwith the water droplet spreading completely and uniformly on the samplesurface within five seconds. When compared with bare glass and thecommercial product, one of the most used photocatalytic glassescurrently on the market, TiO₂-GLASS exhibited a marked improvement inthe wettability properties, as shown in FIG. 2D. The CAs for bare glassand commercial product were found to be 40±10° and 31±5°, respectively.

The performance of the prepared materials was investigated by varyingthe film thickness between 20 and 250 nm. In porous materials, adecrease in the thickness usually causes a dramatic drop inhydrophilicity owing to the poorer density of networked nanostructuresthat are responsible for a quick water adsorption. Conversely, in ournonporous coatings, the hydrophilicity is a surface phenomenon occurringwithout the support of a three-dimensional network. As a result,wettability properties are relatively independent of the thickness, andnotably, samples continued to be superhydrophilic even at the smallthickness of 20 nm, which makes these materials extremely suitable forself-cleaning coatings requiring high optical transparency.

FIGS. 4A, 4B, and 4C show variations of contact angle of tested glassesover time. FIG. 4A shows variations of contact angle of an UV-unexposedTiO₂-GLASS, FIG. 4B shows variations of contact angle of a preliminarilyUV-exposed TiO₂-GLASS that is TiO₂-GLASS which has been preliminarilyexposed to UV, and FIG. 4C shows variations of contact angle of acommercial product, which has been preliminarily exposed to UV, with thecorresponding inset showing the decrease in contact angle undercontinuous UV radiation. Day 0 in FIGS. 4A and 4B refers to the day ofthe annealing treatment for the UV-unexposed TiO₂-GLASS and theTiO₂-GLASS, and Day 0 in FIG. 4C refers to the day of UV treatment forthe commercial product.

Both the preliminarily UV-exposed and UV-unexposed films were kept inthe dark between consecutive measurements (with intervals of 1, 5 or 15days).

Investigations were undertaken in order to study the superhydrophilicstability through wetting-dewetting cycles. Superhydrophilic state wasmaintained for up to five days after the annealing treatment, reaching aplateau at 18±5° after ten days, as shown in FIG. 4A. TiO₂-GLASSreturned to their original wetting behavior after re-annealing with CAsclose to 0°. High-temperature annealing normally results in the removalof organic contaminants that can be responsible for hydrophobicity andwhose effects are unavoidable following environmental exposure.

In order to study the effect of UV radiation on the films, specifically,to assess any possible extension of the superhydrophilic stability overtime, contact angles were monitored for up to 45 days after 30 minutesirradiation of virgin TiO₂-GLASS, and the results were compared to thoseof the same TiO₂-GLASS, which did not undergo any preliminaryirradiation.

After UV exposure, the CA of the preliminarily UV-exposed TiO₂-GLASSremained below 5° for eight days, stabilizing at 13+5° after fifteendays as shown in FIG. 4B. The commercial product reverted back to itsoriginal value of 31±5° in three days after being UV-exposed for thesame time as shown in FIG. 4C, reaching a minimum value of 7±2° undercontinuous UV light soaking as shown in the inset of FIG. 4C.

After aging for 6 months, TiO₂-GLASS and 20-TiO₂-GLASS samples werereannealed and exposed to the extreme weather of Abu Dhabi betweenAugust and September, when temperatures are normally in the range 30-45°C. and the atmospheric dust loading is extremely high. The contact anglewas 22±3° after one month exposure, thereby only increasing by 4.0°compared with the value obtained in indoor environment. Remarkably, evenafter outdoor exposure, TiO₂-GLASS continued to show lower contactangles in comparison with the bare glass (40°) and the commercialproduct (31°).

FIGS. 5A, 5B, 5C, and 5D show images of micro-scale wettabilitycharacterization by. ESEM. FIG. 5A and FIG. 5B are micrographs of thecommercial product before and after the vapor pressure increase from 600to 765 Pa, respectively. The increase in the vapor pressure resulted inwater droplets condensed on the surface. FIG. 5C and FIG. 5D aremicrographs of TiO₂-GLASS before and after the vapor pressure increase,respectively. No difference between FIG. 5C and FIG. 5D was observed.

The wetting behavior of the film surface was explored at the micro-scaleby carefully tuning the vapor pressure inside an environmental SEM(ESEM) and analyzing the resulting water droplets condensed on thesurface. FIG. 5A and FIG. 5B depict the typical micrographs obtainedinside the ESEM chamber for the commercial product. The pressure wasincreased from 600 up to 765 Pa in order to have water condensation andto measure the resulting CA, which was found to be 38±10°, slightlyhigher with respect to the one obtained by traditional contact anglemeasurements. This difference could be due to a different ESEM-chamberpressure compared to environmental pressure and to the lowertemperature. As shown in FIG. 5C and FIG. 5D, TiO₂-GLASS showed noevidence of droplet condensation after increasing the pressure. This isattributable to the extremely low CA, which hampered the formation ofclearly visible droplets even at the micro-scale.

FIG. 6A shows an AFM image, and FIG. 613 shows SEM micrograph ofTiO₂-GLASS. As shown in FIGS. 6A and 6B, the AFM and SEM images of theannealed TiO₂-GLASS highlighted the dense and nonporous structure formedby grains with size of ca. 30-50 nm. No cracks were present, proving theexcellent mechanical stability of the film and the high adhesion to theglass substrate. The root mean square (RMS) roughness was 13.6±1.5 nm,greater than the figure estimated in the as-deposited TiO₂-GLASS(3.7±1.1 nm).

FIGS. 7A and 7B depict size distribution of particles in water sampleswithdrawn from the beaker containing the 20-TiO,-GLASS (FIG. 7A) andfrom the beaker containing the bare glass (FIG. 7B) after ultrasoundtreatment. Water samples were withdrawn at 2.5 and 5 hours and analyzedby a Z-sizer (ZetaPALS, Brookhaven) to verify the possible presence ofsuspended particles. After 5 hours, the used DI water was replaced byfresh water after rinsing the glass samples and the beakers, and thenthe ultrasound treatment was extended by another 2.5 hours.

The adhesion of the 20 nm film to the glass substrate was investigatedby checking the release of film particles into water during ultrasoundtreatment. The water samples were analyzed by a Z-sizer for a properassessment. As shown in FIGS. 7A and 7B, size distribution of theparticles leached out from the bare glass and the functionalized glassthe 20-TiO₂-GLASS) into the water are very similar to each other.Accordingly, it appears that all suspended particles came from theglass, rather than from TiO₂ film, probably from sharp edges of theglass. Notably, after removing the used water including suspendedparticles, washing the bare glass and the 20-TiO₂-GLASS and dipping bothin DI fresh water, the extended ultrasound treatment (up to 7.5 hour,see FIGS. 7A and 7B) did not result in any release of further particles.

FIG. 8 shows Raman spectra of the adhesive tape before (“BARE ADHESIVETAPE”) and after detachment (“ADHESIVE TAPE AFTER DETACHMENT”) from20-TiO₂-GLASS. The spectrum after detachment does not show anycharacteristic TiO₂ peak, and thus confirm the good adhesion of the filmto the substrate.

An adhesive tape was attached to and detached from the 20 nm TiO₂ filmof from 20-TiO₂-GLASS. The surface of the adhesive tape was analyzed byRaman spectroscopy, which is able to detect extremely thin layers ofTiO₂. Referring to FIG. 8, the Raman spectrum of the tape afterdetachment is similar to the one of the bare tape. The main peak ofanatase (145-150 cm⁻¹) is totally missing, and the result points to thestrong attachment of the film to the glass substrate.

The adhesion of the 20 nm film to the glass substrate was also analyzedaccording to the ISO 2409. FIGS. 9A and 9B show optical images of20-TiO₂-GLASS (FIG. 9A) and the commercial product (FIG. 9B) after thecross-cut test according to ISO 2409 standard. Specifically, FIGS. 9Aand 9B show the optical images of the samples after the cross-cut testduring which the coatings were crisscrossed with a cutter to form alattice pattern. Subsequently, an adhesive tape was applied and detachedat a 60° angle. 20-TiO₂-GLASS and the commercial product performedequally, and showed excellent adhesion without any noticeable detachmentof the thin film from the glass substrate. According to ISO 2409standard, the quality of both coatings can be ranked as “0” since theedges of the cuts were completely smooth and none of the squares of thelattice was detached.

A dynamical mechanical analysis was performed in order to check if theglass mechanical properties were affected following the application ofe-beam deposited 20 nm TiO₂ layer. FIG. 10 shows storage moduli of bareannealed glass and 20-TiO₂-GLASS, the functionalized glass. The storagemodulus of the bare glass (˜326 GPa), proportional to the energy storedduring a loading cycle, was only slightly lower than the functionalizedglass (˜335 GPa) over the entire range of temperature (25-250° C.) asshown in FIG. 10. Thus, the mechanical properties of the glass are notaffected by the functionalization with TiO₂, as desired.

Raman spectroscopy was used to investigate the structural properties ofthe prepared samples, the annealed TiO₂-GLASS and the commercialproduct. FIG. 11 illustrates Raman spectra of TiO₂-GLASS and thecommercial product. Raman spectra of the annealed TiO₂-GLASS and thecommercial product confirmed the occurrence of anatase, whosecharacteristic bands were present in both films. E_(g) peaks are due tosymmetric stretching vibrations of O—Ti—O. B_(1g) is due to symmetricbending vibration of O—Ti—O, whereas the A_(1g) is produced byantisymmetric bending vibration of O—Ti—O. A significant shift of 4 cm⁻¹was found for the principal signal, detected at 145 cm⁻¹ in thecommercial product and at 149 cm⁻¹ in the TiO₂-GLASS sample (FIG. 11).This positive shift may be ascribed to the presence of more oxygenvacancies in the TiO₂-GLASS sample, which may induce the reduction oftitanium oxidation state from 4+ to 3+ as a consequence of thedeposition technique and the following annealing treatment. The Ti³⁺ andoxygen vacancies may support the adsorption of water molecules at defectsites and further promote hydrophilicity.

EXAMPLE 4 Antifogging Properties of Non-Porous TiO₂ Films

FIGS. 12A, 12B, and 12C depict antifogging and optical properties ofbare glass, 20-TiO₂-GLASS and the commercial product. FIG. 12A showsthree samples that appeared transparent before the anti-fogging test.FIG. 12B shows anti-fogging characters of bare glass, 20-TiO₂-GLASSafter two months from the thermal treatment and the commercial product.The thermal treatment is discussed in Example 1. FIG. 12C depicts acomparison graph showing UV-vis transmittance data of the commercialproduct and the glass before and after the application of a 20 nm-thicklayer of TiO₂, which slightly changed the transmittance of thesubstrate, leading to a minor shift of the absorption edge.

The antifogging properties, essential when glass is used in indoor andoutdoor humid environments, were tested by placing the samples in adeep-freeze at −15° C. Before the test, all the samples appearedcompletely transparent, with no outward signs of the 20 nm layerdeposited on the glass as shown in FIG. 12A. After 2 hours in thedeep-freeze, the samples were exposed to the humid indoor air, and the20-TiO₂-GLASS sample resulted by far the one with the best antifoggingbehavior thanks to its superhydrophilic character. The lower wettabilityof the commercial product and bare glass caused the moisture to condenseon their surface, resulting in a relatively fogged-up appearance in thecommercial product and occurrence of small droplets in the bare glass.The prepared superhydrophilic films 20-TiO₂-GLASS sample) showed anexcellent water spreading, leading to the formation of a uniform waterfilm. The anti-fogging character of the 20-TiO₂-GLASS was unchanged overtime, as confirmed by the tests performed after two months from thethermal treatment as shown in FIG. 12B.

Optical transparency was investigated in the range 200 nm-800 nm. Asshown in FIG. 12C, the deposition of a 20 nm TiO₂ film on the glass didnot affect the transmittance spectrum significantly over the entirerange of wavelength considered. Indeed, only a minor shift of theabsorption edge was noticed with respect to glass, unlike the commercialproduct sample, which started to absorb markedly below 400 nm. Withregard to the commercial product sample, such difference in theabsorption edge may also result from the thickness of the commercialproduct sample, being much greater than the glass substrate used for20-TiO₂-GLASS. Notably, the refractive index (RI) of the common glass(RI≈1.46) is not affected by the application of a 20 nm thick layer ofTiO, since the optical transmittance of such thin TiO₂ layer is almostidentical to that of the bare glass.

The RI was computed using the Swanepoel method, from the transmissionspectrum, which envelopes around the maxima and minimum were constructedusing parabolic interpolation. FIG. 13A shows UV-vis transmittancespectra of a 250 nm TiO₂ film deposited on glass, and FIG, 13B showsrefractive index of a 250 nm TiO₂ film deposited on glass. The RI versusthe wavelength was obtained by the equations provided by Swanepoelmethod. The RI of 250 nm TiO₂ films, showing appreciable interferencefringes in the transmittance spectrum as shown in FIG. 13A, wasestimated by the Swanepoel method, which is applicable to thin filmsdeposited on transparent substrates that are much thicker than thinfilms as conditions were met in this work. The obtained RI were in therange 2.31-2.01 between 400 and 900 nm as shown in FIG. 13B. Thesevalues are consistent with the ones reported for thin films deposited bysimilar techniques.

EXAMPLE 5 Photocatalytic Properties of Non-Porous TiO₂ Films

FIGS. 14A and 14B show reactivity results of 20-TiO₂-GLASS,outdoor-exposed 20-TiO₂-GLASS (O.E. 20-TiO₂-GLASS) and commercialproduct. Tests were performed in gas-phase under UV light using methanoland 2-propanol as target molecules. FIG. 14A shows the concentrations ofmethanol and formaldehyde monitored over the time, and FIG. 14B showsthe concentrations of 2-propanol and acetone monitored over the time. Itillustrates that the TiO₂ film exhibits a higher photocatalytic activitycompared to the commercial product.

The photocatalytic activity for the degradation of two target organicmolecules, methanol and 2-propanol, was proved in gas phase in oxygenatmosphere. Both target molecules, methanol and 2-propanol, weresuccessfully degraded, and their main organic intermediate (formaldehydeand acetone, respectively) were detected. As illustrated in FIGS. 14Aand 14B, 20-TiO₂-GLASS shows a better performance compared to thecommercial product, resulting in higher conversions and reaction rates.The presence of an elevated density of Ti³⁺ defects in the preparedfilms, as confirmed by the Raman analysis (See FIG. 11), may beresponsible for the higher photocatalytic activity. Indeed, Ti⁺ statescan enhance charge separation and improve light absorption. Finally, allthe reactivity tests were carried out after outdoor exposure of thesamples, which is discussed in Example 3, and, remarkably, thephotocatalytic activity remained broadly unchanged, as depicted in FIGS.14A and 14B.

The above-disclosed subject matter is to be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments, which fall withinthe true spirit and scope of the inventive concept. Thus, to the maximumextent allowed by law, the scope is to be determined by the broadestpermissible interpretation of the following claims and theirequivalents, and shall not be restricted or limited by the foregoingdetailed description.

What is claimed is:
 1. A coated glass comprising a glass substrate; anda TiO₂ film on the glass substrate, wherein the TiO2 film is non-porous,and wherein the TiO₂ film maintains a water contact angle less than 5°in the dark for five days after an annealing treatment.
 2. The coatedglass of claim 1, wherein the TiO₂ film has a thickness of from about 20nm to about 250 nm.
 3. The coated glass of claim 1, wherein the TiO₂film has a thickness of about 20 nm.
 4. The coated glass of claim 1,wherein the water contact angle: of the TiO₂ film stabilizes at lessthan 20° after ten days from the annealing treatment.
 5. The coatedglass of claim 1, wherein the water contact angle of the TiO₂ film isless than 5° for eight days from the annealing treatment andUV-exposure.
 6. The coated glass of claim 1, wherein the water contactangle of the TiO₂ film stabilizes at less than 15° after fifteen daysfrom the annealing treatment and UV-exposure.
 7. The coated glass ofclaim 1, therein the TiO₂ film has a grain size of from about 30 nm toabout 50 nm.
 8. The coated glass of claim 1, wherein the TiO₂ film has aroot mean square (RMS) roughness of about 13 nm.
 9. The coated glass ofclaim 1, wherein the coated glass has optical transmittance greater than85% at wavelength higher than 350 nm.
 10. The coated glass of claim 1,wherein the coated glass shows higher water spreading characteristicthan the glass substrate after exposure to humid indoor air following 2hours in a freezer at −15° C.
 11. The coated glass of claim 1, wherein adifference between storage modulus of the coated glass and storagemodulus of the glass substrate is less than 20 Gpa.
 12. The coated glassof claim 1, wherein the coated glass reduces a molar concentration ofmethanol by about 60% when the coated glass is tested in gas phase inoxygen atmosphere and is exposed to UV light for about 30 hours.
 13. Thecoated glass of claim 1, wherein the coated glass reduces a molarconcentration of 2-propanol by about 20% when the coated glass is testedin gas phase in oxygen atmosphere and is exposed to UV light for about30 hours.
 14. The coated glass of claim 1, wherein the TiO₂ film isimpervious to water.
 15. A coated glass comprising: a glass substrate;and wherein the TiO2 firm is non-porous, and a TiO₂ film on the glasssubstrate, wherein the TiO₂ film has a grain size of from about 30 nm toabout 50 nm.
 16. The coated glass of claim 15, wherein a root meansquare (RMS) roughness of the TiO₂ film is about 13 nm.
 17. The coatedglass of claim 15, wherein the TiO₂ film maintains a water contact angleless than 5° in the dark for five days after an annealing treatment. 18.The coated glass of claim 17, wherein the water contact angle of theTiO₂ film stabilizes at less than 20° after ten days from the annealingtreatment.
 19. The coated glass of claim 15, wherein a water contactangle of the TiO₂ film is less than 5° for eight days from an annealingtreatment and UV-exposure.
 20. The coated glass of claim 19, wherein thewater contact angle of the TiO₂ film stabilizes at less than 15° afterfifteen days from the annealing treatment and UV-exposure.
 21. Thecoated glass of Claim 15, wherein the TiO₂ film has a thickness of fromabout 20 nm to about 250 nm.
 22. The coated glass of claim 15, whereinthe TiO₂ film has a thickness of about 20 nm.
 23. The coated glass ofclaim 15, wherein the coated glass has optical transmittance greaterthan 85% at wavelength higher than 350 nm.
 24. The coated glass of claim15, wherein a difference between storage modulus of the coated glass andstorage modulus of the glass substrate is less than 20 Gpa.
 25. Thecoated glass of claim 15, wherein the TiO₂ film is impervious to water.